BIOLOGICAL, SEROLOGICAL, AND GENETIC-CHARACTERIZATION OF HIV-1 SUBTYPE-E ISOLATES FROM NORTHERN THAILAND

Twenty-three HIV-1 isolates were recovered from PBMCs from 26 HIV-1-se ropositive individuals in northern Thailand. The viruses grew readily in human PBMCs but only 7 of 17 (41.2%) and 5 of 17 (29.4%) replicated and only at a low level in primary macrophages and in established T c ell lines, respectively. By immunoblot assays, sera from Thai subjects were strongly reactive with gp120 from a Thailand isolate, moderately reactive with a Rwandan isolate, and weakly reactive with a North Ame rican strain. These three viruses represent, respectively, examples of subtypes E, A, and B as classified by the sequences of the envelope r egion.(1) Serological assays indicated that broadly reactive rather th an type-specific neutralizing activity was detected among these northe rn Thai sera. The majority of the sera (approximately 75%) neutralized a representative Thailand isolate and the Rwanda isolate but only 55% neutralized the North American strain. However, the difference was no t statistically significant. The genetic analyses indicated that nearl y all the Thai isolates were highly homogeneous and distinct from the North American/European consensus sequence (subtype B); they belong to subtype E. This if the first report providing biological, serological , and genetic characterization of HIV-1 strains from Thailand. The fin dings suggest these viruses were recently introduced into the country and that serological evaluation of viral strains needs to be considere d along with genetic subtyping when developing an HIV-1 vaccine.